1. Field of the Invention
This invention relates to the field of apparatus and method for the precisely controlled and coordinated supply of sheath stream and sample fluids to sheath stream flow cell systems, such as high-speed automated biomedical analytical systems.
2. Description of the Prior Art
Although apparatus and methods are known for the supply of sheath stream and sample fluids to sheath stream flow cells, none accomplish these functions in a precisely controlled and coordinated manner using the same sheath stream flow cell, and associated detecting and pumping means, for successive different types of sample analyses.
In many instances in the prior art peristaltic pumping is used to supply the sample fluid stream to the flow cell. This is disclosed, for example, in U.S. Pat. No. 3,740,143, wherein multi-channel peristaltic pumping is used to supply respective series of diluted blood samples to a plurality of sheath stream flow cells for a different type of sample analysis with respect to each. This leads to less than optimal accuracy in cell analyses due to marginal variations in peristaltic pump roller and pump tube dimensions, which cause variations in the diameter, velocity and/or volume of the sample fluid stream through the flow cell. Since separate pumping systems are used, with the sheath stream fluid being pressure pumped from a constantly pressurized source, variations in the essential sheath-sample fluid streams flow and volume ratios can also occur to further degrade sample analysis accuracy. In addition, peristaltic pumping requires frequent and precise calibration; while the relatively long lengths of peristaltic pump and supply tubing markedly increase the potential for sample carryover. Carryover is defined as the contamination of a succeeding sample by the residue of a preceding sample resulting in loss of accuracy. Further, peristaltic pumping, which operates by the occlusion or squeezing of the pump tubes by the pump rollers, can and does result in damage to the integrity of cells or like sample fluid particles to further degrade accuracy. Too, the requirement for separate sheath stream flow cell and associated optical and electronic detecting means, and a separate sample pumping channel, for each different type of sample analyses to be performed, add very significantly to overall complexity and cost of such analytical system.
Although more current efforts have been made to remedy some of the above-described problems through utilization of separate, finely calibrated peristaltic pumps for each of the sheath stream and sample fluids as described, for example, in paper HYDRODYNAMICS OF CONCENTRIC PERISTALTIC LAMINAR FLOW OF TWO DIFFERENT FLUIDS by K. Uffenheimer and I. Beretsky, M.D., presented at the Mar. 23, 1973 meeting of The American Association For Medical Instrumentation at Chicago, Ill., these efforts have not proven fully satisfactory, especially in increasingly sophisticated automated biomedical analytical systems. Again, separate sheath stream flow cell and associated detecting and pumping means are contemplated for each different type of sample analysis to be performed.
Other apparatus and methods are known for the supply of sheath stream and sample fluids to a sheath stream flow cell and, as disclosed in U.S. Pat. No. 3,661,460, use a combination of gravity feed, peristaltic pumping and vacuum pumping, requiring liquid trap, pressure regulation, pressure gauge, and needle valve or other flow restrictor means, to those ends. These apparatus and methods can be difficult to calibrate and tend not to remain calibrated, and thus have also not proven fully satisfactory, especially in increasingly sophisticated automated biomedical analytical systems. Again, a separate sheath stream flow cell, and associated detecting and pumping means, are required for each type of sample analysis to be performed.
Apparatus and method for the precisely controlled and coordinated supply of sample and sheath stream fluids under optimal conditions to maximize the accuracy and reproducibility of successive sample analyses are disclosed in the copending application of Gregory A. Farrell entitled New And Improved Volumetric Pumping Apparatus And Method For Supplyinq Fluids To Sheath Stream Flow Cells, Ser. No. 408,390, filed Aug. 16, 1982, now abandoned, and assigned to the assignee hereof. There too, however, a separate sheath stream flow cell and associated detecting and pumping means is required for each different type of sample analysis to be performed.
Sheath stream flow cell analysis apparatus utilizing a selector valve to permit somewhat different types of sample analyses by the same sheath stream flow cell are known in the form of the hematology instrument "Ortho ELT8" as manufactured by Ortho Diagnostic Systems, Inc. of Westwood, Mass. However, this instrument utilizes independent and complex sample fluid supply channels, rather than separate sample fluid sources, for different sample analyses, thereby requiring at least one separate sample fluid pump for each sample fluid analysis of interest with resultant increase in the overall complexity, cost and maintenance requirements of the apparatus. This also increases sample carryover. Too, no provision is made in this apparatus for the selection and supply of different sheath stream fluids to the flow cell whereby successive markedly different types of sample analyses, requiring in turn markedly different types of respectively optically compatible sheath stream fluids, cannot be performed thereon. Also, no provision is made in this apparatus for the precisely coordinated and controlled differential pumping of the sample and sheath fluids to the flow cell, thus rendering extremely difficult, if not impossible, the true optimization of the accuracy and reproducibility of the sample analysis results.